1. Field of the Invention
The present invention relates to a vaporizer (vaporized gas generating oven) for an ion source which is used for ionizing a solid source in an ion implantation apparatus.
2. Description of the Related Art
In the manufacturing of semiconductor wafers, an ion implantation apparatus ionizes impurity atoms, accelerates the ions at high energy for implantation into a semiconductor to dope the impurities thereinto.
The ionization of impurity atoms may employ a solid source and a gaseous source. Generally, the ionization of a solid source involves placing the solid source in a crucible or a melting pot within a vaporizer of an ion source station, heating the solid source with a heater for vaporization, delivering the vaporized source into an arc chamber of the ion source station through a nozzle having a gas inlet port formed in the crucible, and ionizing the vaporized source by a plasma in the arc chamber.
The solid source placed in the vaporizer, for example, arsenic (As) is heated to approximately 370° C. in vacuum with a heater for vaporization. The vaporized As is delivered into the arc chamber through the nozzle by a pressure difference between vacuum conditions in the crucible of the vaporizer and in the arc chamber.
Japanese Patent Application Kokai No. 07-320671 shows a method of rapidly vaporizing a solid source using a microwave. Japanese Patent Application Kokai No. 2002-100298 in turn shows a method which enables rapid cooling for switching one source to another by providing a cooling duct spirally wound around a vaporizer.
However, when a solid source having a heavy mass, for example, solid As, is used, a desired amount of gas cannot be introduced into an arc chamber according to vacuum conditions in an ion source station, even if the solid source is heated in the vaporizer and vaporized, resulting in large variations in the amount of vaporized As.
Therefore, As must be vaporized more than a required vapor pressure in some cases for ionizing the gas introduced into the arc chamber to generate an ion beam required for implantation. In this event, there was a problem that As not introduced into the arc chamber is solidified and sticks around the nozzle, causing clogging of the nozzle and burn-in.